The present invention relates to aircraft landing-gear and more particularly to skid-type landing-gear for rotary-wing aircraft.
Prior art skid-type landing-gear consisted basically of two main skids parallel to each other and made up of one or more sections.
Such skids are usually connected to the aircraft's structure through the use of either hinged supports, certain elements of which include damping means, or of arcuate fixed supports possessing sufficient natural flexibility to attenuate the effects of sudden hard contact with the ground.
The presence of hinged supports including for example damping means of the hydraulic or pneumatic type considerably increases the cost and complexity of the landing-gear. In addition it necessarily diminishes the reliability of the aircraft because the bulk of skid supports equipped in this manner, notably
The use of simplified gear comprising two main one-piece skids connected to two flexible arcuate supports positioned in front of and behind said skids, respectively, and rigidly connected to the aircraft structure permits alleviation of the drawbacks mentioned above.
However, such a simplified landing-gear does not always fully meet certain requirements specific to this type of landing-gear primarily concerned with the behavior of the aircraft during maneuvers close to the ground. For instance, in addition to being capable of absorbing a certain amount of energy, the landing-gear, when in contact with the ground, must not give rise to the vibration phenomenon known as `ground resonance`, which consists in divergent oscillations of the whole aircraft on its landing-gear. These oscillations are excited by the alternating movements of the main-rotor blades in the rotation plane of the rotor, which movements are termed drag motion.
The onset of this ground resonance phenomenon can be greatly encouraged on a helicopter equipped with a skid landing-gear by the nature and condition of the surface of the landing or take-off area (e.g. concrete or earth surfaces, or imperfectly flat surfaces).
This being so, there can be infinity of conditions under which the landing-gear contacts the ground: contact, for example, can be made at four points, three points, or only at two points in the case of a partial landing. Certain of these conditions may not ensure clear stability of a helicopter and induce oscillations that rapidly become dangerously divergent for both the machine and its occupants.
The present invention provides for better adaptability of the skids to the nature of the surface of the landing area and thereby avoids a great many possible forms of contact liable to engender ground resonance.